Simulation Variables

SimVars are “simulation variables” and they are the way that third party APIs and add-ons can get information about the current state of the simulation. In general these variables are used to control aircraft behaviors by permitting you to retrieve data about things like weather conditions, position, or aircraft status, and in many cases they can also be used to modify something within the simulation, in particular aircraft instruments and controls - although they can also have many other purposes within any add-on package.

You can find detailed information about each particular SimVar on the following pages:

• Simulation Variable Units
• Camera Variables
• Services Variables
• Miscellaneous Variables
• Aircraft SimVars:
  • Aircraft Autopilot/Assistant Variables
  • Aircraft Brake/Landing Gear Variables
  • Aircraft Control Variables
  • Aircraft Electrics Variables
  • Aircraft Engine Variables
  • Aircraft Flight Model Variables
  • Aircraft Fuel Variables
  • Aircraft Miscellaneous Variables
  • Aircraft Radio Navigation Variables
  • Aircraft System Variables
  • Helicopter Variables
  • Balloon Variables

We have a Visual Studio project that can be used to generate the SimVar Watcher tool, which can be used to monitor and edit SimVars as the simulation runs. You can find full details here:

• SimvarWatcher

There is also a further section dedicated to Event IDs. These are used as a way to interface between different simulation systems, with the user at the top level the various sub-systems within the simulation at the bottom. You can find all these event IDs in the following section:

• Event IDs

Finally, there is an additional document for Audio Design that lists the RTPC events and the SimVars they are associated with:

• RTPC And Simulation Variables

SimVar Index#

Below you can find indexed all the SimVars available, presented this way to facilitate finding the required variable at a glance or through the search system:

A#

B#

C#

D#

E#

F#

G#

H#

I#

J#

K#

L#

M#

N#

O#

P#

R#

S#

T#

U#

V#

W#

Y#

Z#

Convenience SimVars#

Within the simulation variables, there are some which we have labeled as convenience SimVars. What this means is that while the SimVar exists within the code and can be used like any other SimVar, it has no effect on the actual simulation and is there as a convenience for you to use in custom logic. This just means just means that any behaviour you want the SimVar to have must be created by you though the use of programmed logic in the model behaviour files, JS, or WASM.

Note on SimVar Data Types#

When accessing SimVars using the SimConnect API, you would first create a data definition using the function SimConnect_AddToDataDefinition and in that you would tell the simulation the data type for the variable. By default this is a 64 bit float, but for most simulation variables this can be almost any appropriate data type (that fits the unit of the SimVar) and the same data type should be used when getting or setting the value later. When a specific data type is required - for example SIMCONNECT_DATA_LATLONALT - this will be mentioned in the description for the variable.

Note On SimVars In Multiplayer#

Previous iterations of Flight Simulator permitted the communication of SimVars between aircraft when multiplayer was active, either within a shared cockpit or to all aircraft. However Microsoft Flight Simulator 2024 does not have the same concept of shared cockpit as previous versions, as such only a small number of variables are communicated between all aircraft. The table below lists all of these variables, and they are also flagged within the SimVar descriptions on their respective pages. Note that the SimVars are split into two categories where:

• Near: these SimVars are transmitted to all aircraft within a 500m radius.
• Far: these SimVars are transmitted to all aircraft up to a maximum radius of 10,000m.

NEAR (up to 500m)#

FAR (up to 10,000m)#

Simvar Watcher#

An essential tool when working with the various simulation variables and setting up an aircraft is the Simvar Watcher tool:

This tool permits you to connect to the simulation in real-time and view the values of almost any SimVar available, as well as set the SimVar to a different value (if the SimVar is settable). Find out more information on this useful tool here:

• SimvarWatcher

SimVars And RPN#

When creating add-ons for aircraft - primarily Instruments - you will need to be able to access Simulation Variables and change them based on user input in the form of Key Events. Both using SimVar values and using input key events is done using operations written in RPN, as explained below. Note that you can also find many use-cases and examples in the different ModelBehavior templates.

SimVars permit you to get the state of a component, or the state of something in the simulation, and they are generally accessed using the following RPN format:

(A:[simvar_name]:[simvar_index], [units])

Note that the “index” value is only required by a few SimVars. Here are some simple examples:

(A:SIM ON GROUND, Bool)
(A:AIRSPEED TRUE, Knots)
(A:TURB ENG IGNITION SWITCH EX1:1, Enum)

It should be noted that sometimes you will see simulation variables written using snake case, and prefixed with SIMVAR_, as that is how they appear in the simulation code itself. However when using them in RPN, you should omit the SIMVAR part as well as the _. For example:

SIMVAR_CIRCUIT_ON -> (A:CIRCUIT ON:1, Bool)

SimVars With Multiple Parameters#

Some simvars will require multiple parameters in order to retrieve the expected value. One such example is WEAR AND TEAR LEVEL, which is designed to retrieve the current wear status of a part of the aircraft. However to specify which part to query you will need to provide both the type of the part you are interested in, and the index of that part. For example, say you want to query about the state of the second piston engine. For that you would first need to provide it the value 39 - which is the number that corresponds to the piston engine as explained here: Wear And Tear Component IDs. You would then need to provide a second value which corresponds to the piston engine you wish to retrieve the wear of, in this case 2. Using RPN, this would be done as follows:

2 (A:1:WEAR AND TEAR LEVER:39, Percent)

Here the SimVar “index” is used to send the first parameter as usual for other SimVars with a single parameter. The second parameter, however, requires you to specify how many extra values should be popped from the stack and sent to the SimVar. This is done by adding the value 1 into the A: variable definition, which indicate that you want to pop one parameter. This parameter value is specified to be 2.

In rare cases, the second parameter for the SimVar is retrieved from another SimVar. This is commonly found when working with the electrical system, for example the SimVar CIRCUIT CONNECTION ON requires a circuit index and a bus index, with the bus index coming from the SimVar BUS LOOKUP INDEX. The RPN for this would be written like this:

2 (>A:BUS LOOKUP INDEX, Number) (A:CIRCUIT CONNECTION ON:45, Bool)

Using Indexed Parameter Names#

Many components in the various systems for an aircraft are indexed and also named. In previous version of the simulation, the index was what you would use in a SimVar to refer to the component, however with the introduction of modular SimObjects, indices are no longer reliable as they can change as part of the merge process. To make sure you are referencing the correct component now, you you can (and should) use the name of the component, rather than its index (and components should all be unique).

Using the name instead of an index follows this format:

<SIMVAR>:'<NAME>'_n

So, for example, using the HYDRAULIC VALVE ACTIVE SimVar, we would have something like the following:

(A:HYDRAULIC VALVE ACTIVE:'VALVE_GEAR_LEFT_1'_n, Bool)